1. Field of the Invention
This invention relates to circuits and methods for transmission and reception of digital data communication signals. More particularly, this invention relates to circuits and methods for interleaving, compression, duplication, transmission, and recovery of frames of digital data communication signals.
2. Description of Related Art
As is known in the art, the Federal Communications Commission (FCC) allowed type-approved and unlicensed use for a shared and lower-tier occupant in the industrial, scientific, and medical (ISM) radio bands around 915 MHz, 2.442 GHz, and 5.750 GHz. This allocation of the radio spectrum has spurred increased use of spread-spectrum communications. The fact that this radio spectrum allocation is shared is important. Other users, and therefore other signals, either fixed frequency or spread spectrum, are present in these ISM bands and may cause radio frequency (RF) interference.
RF interference is caused by un-wanted RF signals occupying at the same frequency as an intended signal thus resulting in a loss of information—either audio or digital data. The key factors that effect the level of RF interference are the relative signal strength between the intended and the unwanted signal, the bandwidth of the unwanted signal that of the intended signal, the relative time that the unwanted signal occupies the same bandwidth as the intended signal. The relative signal strength is typically defined under an RF co-channel selectivity specification. The relative time that the unwanted signal occupies the same bandwidth relates typically to Frequency Hopping Spread Spectrum (FHSS) transmission systems when the FHSS transmission systems are occupying the same bandwidth as that of a fixed frequency transmission system.
Since the ISM radio bands are unlicensed, the fixed frequency applications are for example wireless networking solutions, radio frequency identification tags, alarm systems, and security monitoring, home automation, garage door openers, automatic meter reading, and remote sensors, and digital audio transmission. Similarly, the FHSS ISM band applications include digital wireless networking such as Bluetooth network, cordless telephones, and microwave telecommunications. The fixed frequency applications divide the ISM radio bands into separate channels or sub-bands.
Each fixed frequency application occupies one of the channels or sub-bands and is isolated from other nearby applications occupying other channels or sub-bands. The FHSS applications divide the ISM radio bands into similar channels, but with narrower bandwidth and occupy each of the channels for a short period of time. The FHSS applications hop from channel to channel in a prescribed hopping pattern such as a pseudo random hopping pattern and may actually interfere with a fixed frequency application for sufficient time to cause interruption in the application. For instance the Bluetooth specification divides the ISM radio band into 79 channels with a 1 MHz bandwidth. The Bluetooth specification calls for the transmitter to make 1600 hops from channel to channel per second. If a fixed frequency application divides the ISM band into 10 channels, a Bluetooth transmission may occupy the fixed frequency band 6.25 msec of every second. This is sufficient to cause distortion and errors in the fixed frequency application.
“Interference Rejection in Digital Wireless Communications”, Laster, et al., IEEE Signal Processing Magazine, May 1997, Vol.: 14, Issue: 3, pp.: 37-62 comprises a literature review of published papers pertaining to single-channel adaptive interference rejection in digital wireless communication. Techniques for the suppression of co-channel interference are discussed for spread spectrum frequency hopping transmission schemes and non spread spectrum schemes.
“Cochannel Interference Suppression Through Time/Space Diversity” Calderbank et al., IEEE Transactions on Information Theory, May 2000, Vol.: 46, Issue: 3, pp.: 922-932 describes how to achieve interference suppression and mitigation of fading through diversity in time provided by channel coding. The mathematical description of time diversity is identical to that of space diversity, and what emerges is a unified framework for signal processing. Decoding algorithms are provided for repetition codes, rate 1/n convolutional codes, first-order Reed-Muller codes, and a new class of linear combination codes that provide cochannel interference suppression. In all cases it is possible to trade performance for complexity by choosing between joint estimation and a novel low-complexity linear canceller structure that treats interference as noise.
“Rejection of Bluetooth Interference in 802.11 WLANs”, Soltanian et al., Proceedings IEEE Vehicular Technology Conference, 2002. Vol.2, pp.: 932-936 vol.2, investigates the use of complex coefficient adaptive filters for interference suppression in the direct sequence spread spectrum IEEE 802.11 b system. The parameters of a recursive least-squares lattice filter are determined to mitigate the effect of a hopping narrowband interferer such as Bluetooth.
U.S. Pat. No. 5,692,018 (Okamoto) describes an interference canceller that has a complex multiplier for multiplying a signal recovered from a quadrature modulated carrier by a correlation value, and a another complex multiplier for multiplying a delayed version of the recovered signal by a another correlation value. The outputs of the multipliers are additively combined in an adder and subtractively combined in a subtractor. The output of the adder is amplified by an AGC amplifier to produce a reference signal representative of the envelope of the adder output. First correlation between the recovered signal and the reference signal is detected and the first correlation value is derived. A second correlation is detected between the delayed version of the recovered signal and the reference signal and the second correlation value is derived. One of the outputs of the amplifier and the subtractor is selected by a selector. A decision feedback equalizer operates on the output of the selector to produce a decision output and a decision error. The decision error is compared with a threshold value and the selector is controlled depending on whether the decision error is higher or lower than the threshold value.
U.S. Pat. No. 5,694,438 (Wang, et al.) teaches a method and apparatus for managing a data symbol received in a time diversity communication system. A current data symbol is received by a receiver in a frame of data of a time diversity communication system. A symbol counter counts a signal from a symbol clock synchronized to the frame of data to provide a count of the current data symbol, and a bit line translator maps a current address from the count. A conditional processor derives a selected memory address from the current address. Then, based upon the current address, a comparator makes a choice among storing the current data symbol in a memory at the selected memory address, merging the current data symbol with an earlier received data symbol stored at the selected memory address during an earlier frame of data, and ignoring the current data symbol.
U.S. Pat. No. 5,850,419 (Todoroki) details a time diversity communication system. In the time diversity communication system, loss of data or generation of incorrect data may occur due to, for example, the shadow effect. On the transmission side, an interlaced signal is generated in which the input digital signal string is combined with the same signal string delayed by n bits, k redundancy bits are added to every m bits of this signal, the signal is divided into blocks of (m+k) bits, an interleaving process is executed for every j blocks in which unique words are added, following which the signal is transmitted. On the receiving side, unique words are detected, a de-interleaving process is performed, and a check is made for the presence of error signals. The delayed and non-delayed signals are next separated from the decoded data, and depending on the state of the signals, the desired signal is selected at selector and outputted. A conformity judgment circuit judges conformity with the separated signal determined to be effective using effective gate signals indicating the effectiveness or ineffectiveness of decoded data, performs switching control of the separated signals, and monitors synchronization.
U.S. Pat. No. 5,883,928 (Eaton) describes a time diversity radio communication system. The time diversity system includes a radio receiving device. The time diversity system receives a temporary address, a group message associated with the temporary address, and an instruction vector for activating the temporary address as original information and, subsequently, duplicate information in a radio signal having frames of data. When the original instruction vector is not received by the receiving device, a later frame is searched for the duplicate instruction vector, which, when located, activates the temporary address stored by the receiving device. The receiving device then determines which frame is capable of reception by the receiving device includes the group message and the receiving device searches for the temporary address and the group message in that frame. The temporary address is then deactivated.
U.S. Pat. No. 6,301,313 (Gevargiz, et al.) teaches a mobile digital radio system. A plurality of satellites and terrestrial repeaters transmit substantially identical information that is contained in an original time division multiplexed data stream. Each satellite transmits on a separate frequency band, and all terrestrial repeaters transmit on one shared frequency band. A mobile receiver simultaneously processes the frequency bands. The receiver selectively parses and concatenates a plurality of time division multiplexed data streams to substantially recompose the original data stream. The output may be a high fidelity audio signal, data for display, or a combination of audio and displayed data.